This invention relates to glass compositions, typically niobium and lead containing, having properties which render the compositions useful in fiber optic faceplate applications, e.g, as electro-optical image tubes, fiber optic image inverters, fiber optic couplers, high efficiency, high contrast rear projection screens, and image couplers for various solid state arrays, field flatteners, image converters, and tapers.
A fiber optic faceplate is an optical mosaic in which fibers are fused together to form a vacuum-tight glass plate. Such a glass plate is effectively equivalent to a zero-thickness window since the image formed on the inside surface of a vacuum enclosure is transported to the external surface with a minimum loss of light. Because of this basic function, fiber-optic faceplates are frequently used to replace ordinary glass viewing areas in vacuum tube envelopes. They can also be used to advantage for field flattening, distortion correction, ambient light suppression and control of angular distribution. Common applications include image intensifiers, storage tubes, and special orthicon and vidiocon tubes.
Many fiber optic glass compositions are known. See, e.g., U.S. Pat. Nos. 3,460,954; 3,503,764; 3,513,004; 3,616,766; 3,650,780; 4,099,834; and 4,194,807. Several of these patents disclose that the composition should be substantially free of lead. See, e.g., U.S. Pat. Nos. 3,460,954; 3,503,764 and 3,616,766.
A need has remained to further the development of fiber optic glasses, e.g., to improve the properties for advanced applications such as fiber optic faceplates.